1. Field of the Invention
This invention relates to a wireless LAN (Local Area Network) terminal and a handover method thereof for resolving a sound cutoff and image cutoff which occur when a terminal is moved.
2. Description of the Related Art
In a wireless LAN system, when a terminal participates in a basic service set, steps of three stages or a scanning, an authentication, and an association are performed. In case the terminal shifts from one basic service set to another basic service set with the communication being continued, the terminal connected to one base station is reconnected to another base station. In case the terminal determines that it cannot continue the communication with a base station to which the terminal is currently connected, the terminal searches for a new base station by performing the scanning and performs a reassociation.
Accordingly, when an information terminal such as a personal computer or a PDA (Personal Digital Assistant), which is connected to a wireless LAN, moves, due to the handover for switching a wireless LAN access point, the reauthentication has to be performed for the handshake.
Furthermore, there is a high speed handover method under which a cordless handset directly accesses access points capable of communicating at the periphery thereof to take in the access point information, retains the latest information of the communicable access points in a database, and takes in an access point from the communicable access points by utilizing the latest information of the database when starting the handover, which can increase the handover completion rate of the selected handover destination access point (For example, Patent Document 1: JP-A-2004-88592).
Furthermore, there is also a wireless terminal authentication method which reduces the time period required for the authentication when a wireless terminal is moved in wireless networks (For example, Patent Document 2: JP-A-2004-266331).
Meanwhile, in a wireless LAN system, when the handover is performed while a wireless LAN terminal is transmitting packets at the time of, for example, a voice communication, there may be packet loss since the authentication sequence of the wireless LAN is performed, which interrupts the data transmission.
For example, when making a video phone call using a personal computer, there is a case that the sound cutoff and image cutoff for several hundreds milliseconds or more are caused at the time of switching a wireless LAN access point. Accordingly, there are needs for resolving the sound cutoff and image cutoff brought about when a terminal is moved so as to facilitate the IP (Internet Protocol) telephone call and IP-based TV (television) conference.